1. Field of the Invention
The present invention relates to a camera that has a continuous photographic mode and that performs automatic focus adjustment on a moving subject.
2. Background of Related Art
A conventional single lens reflex camera predicts the subject position at the time of exposure when the subject is a moving subject and drives the lens to a corresponding focus position.
When continuously photographing a moving subject, the single lens reflex camera lowers the mirror after completing the photograph, and immediately performs focus state detection after the subject image is stabilized. Lens driving is started based on the focus state detection result. Continuous photography of a moving subject in a conventional camera is performed by making the assumption of constant frame intervals that indicate the time from the start of the photograph to the completion.
However, when the shutter preparation (shutter charge) time or the film supply time is delayed during continuous photography because of a drop in the voltage of the camera power source by more than a predetermined time interval, the time between interval frames changes. During continuous photography, in this case, a conventional automatic focus camera having a constant frame interval still drives the lens according to the premise that the photographic preparation sequence (shutter preparation and film supply) completes in a predetermined time. Thus, when the photographic preparation sequence does not complete in the predetermined time, the subject image plane position at exposure deviates. Therefore, an out of focus photograph results.
The present invention provides an automatic focus camera that maintains precise automatic focus adjustment when the photographic preparation sequence, including at least the shutter action preparation and film supply preparation, is not completed in a fixed time. In other words, the frame interval time can change because of certain factors and precise automatic focus is maintained.